Aliyah, transliterated from the Hebrew עלייה, which literally translates as "ascent", is the term used in reference to the Jewish immigration to the state of Israel; the term pre-dates the 1948 founding of modern Israel.
The opposite (Jewish emigration from Israel) is known as Yerida or "descent".
Since the founding of the State of Israel, Aliyah has increased significantly, in some cases involving wholesale relocations of entire Jewish communities from countries hostile to Israel (or undergoing civil unrest of their own). This is due in large part to the Law of Return, which gives any person of Jewish ancestry (with extremely few exceptions, such as persons having a criminal background) the legal right of Aliyah to Israel.
The Jewish Agency for Israel is the major non-profit agency funding Aliyah.